Tunnels and other underground facilities are integral parts of our transit, highway, water, and wastewater infrastructure that society relies on. Some of these facilities are critical lifelines that must remain operational or be returned to service quickly after an extreme seismic event to prevent loss of life. In areas subject to earthquakes, WSP routinely performs seismic analysis and design for tunnels and underground facilities to meet these challenges while also addressing seismic resilience, and sustainability in the design and retrofitting of existing tunnels and underground facilities. This involves cross-disciplinary interactions with planners, architects, owners, agencies, decision makers, and the affected public at large.

In general, earthquakes can produce two distinct types of effects on underground structures, ground shaking and ground failure. Tunnels are generally considered among the safest structures during earthquake ground shaking, because as ductile embedded structures they tend to move with the ground in responding to the shaking. WSP has extensive experience of designing tunnel linings to accommodate the seismic ground deformations without overstressing which is fundamental to providing a resilient structure that will perform acceptably during an earthquake. Ground failure places more significant demands on tunnels and underground structures such as fault displacement, liquefaction, land sliding, lateral spreading, and settlement. WSP employs state of the art techniques to address these hazards often using sophisticated two-and three-dimensional numerical models to analyze the performance of these structures. Thorough site characterization is critical to provide the data needed to accurately characterize the site for these analyses and design.

Globally, the WSP approach to tunnelling design is moving towards a new mindset that addresses the threats of extreme earthquake, multi-hazard, and man-made events in an infrastructure system by incorporating resiliency and “fail-safe” capabilities that allow continuing operation or quick return to service in the event of an incident. This often entails designing for structural ductility under the collapse avoidance limit state scenario.